How do we know that leaven represents false doctrine?

Leaven signifies not just physical yeast but a spiritual concept of corruption. In Matthew 16:8-12, Jesus warns his disciples to beware of the leaven of the Pharisees and Sadducees, indicating that their teachings were corrupt and misleading. This metaphor is consistently used throughout Scripture, highlighting that even a small amount of false teaching can corrupt the whole community of believers. The Apostle Paul reinforces this idea in 1 Corinthians 5:6, stating that 'a little leaven leaveneth the whole lump,' illustrating the infectious nature of false doctrine within the church.